In known types of nuclear power reactors, for example as used in the Dresden Nuclear Power Station near Chicago, Ill., the reactor core comprises a plurality of spaced fuel assemblies arranged in an array capable of self-sustained nuclear fission reaction. The core is contained in a pressure vessel wherein it is submmerged in a working fluid, such as light water, which serves both as coolant and as a neutron moderator. Each fuel assembly comprises a tubular flow channel, typically of approximately square cross section, surrounding an array of elongated, cladded fuel elements or rods containing suitable fuel material, such as uranium or plutonium oxide, supported between upper and lower tie plates. The fuel assemblies are supported in spaced array in the pressure vessel between an upper core grid and a lower core support plate. The lower tie plate of each fuel assembly is formed with a nose piece which fits in a socket in the core support plate for communication with a pressurized coolant supply chamber. The nose piece is formed with openings through which the pressurized coolant flows upward through the fuel assembly flow channels to remove heat from the fuel elements. A typical fuel assembly of this type is shown, for example, by D. A. Venier et al. in U.S. Pat. No. 3,654,077. An example of a fuel element or rod is shown in U.S. Pat. No. 3,378,458.
A plurality of control rods, containing neutron absorbing material, are selectively insertable in the spaces or gaps among the fuel assemblies to control the reactivity of the core. In a known core arrangement, such as shown for example in U.S. Pat. No. 3,020,888, the control rod blades have a cross or cruciform trasversel cross section shape whereby the "wings" of the blades of each control rod are insertable in the spaces between an adjacent four fuel assemblies. Suitable mechanisms are provided, as shown in the above-mentioned U.S. Pat. No. 3,020,888, to selectively move the control rods into and out of the core whereby the neutron population and hence the core power level can be controlled by the non-fission capture of neutrons by the neutron absorbing material in the control rods. Suitable such neutron absorbing materials, including commonly used boron, are set forth in the above-mentioned U.S. Pat. No. 3,020,888.
During initial operation of the first core of a reactor, temporary, removable control curtains may be used to augment the moveable control rods. Such curtains may be formed of a boron stainless steel alloy and be suspended from the upper core support grid in the water gaps opposite the control blade tips.
Additional information on nuclear power reactors may be found, for example, in "Nuclear Power Engineering," M. M. El-Wakil, McGraw-Hill Book Company, Inc., 1962.
While the various reactor components are thoroughly factory tested before being placed in the reactor, there is a continuing need for in-service inspection equipment which can rapidly and conveniently verify the integrity of or detect any anomalies in such components at the reactor site, particularly after such components have been subjected to reactor service and have, therefore, become radioactive. Such radioactive condition of used components requires remotely operable equipment which can scan such components under water to protect the test equipment operators from radiation. Furthermore, known component testing techniques using photographic film, such as X-ray techniques, are not useful for radioactive components because the film is exposed by the radiation therefrom.
It is known that neutrons can be detected in the presence of radiation from radioactive components. It is also known that the transmission of neutrons through a component is a function of the neutron absorbing properties of the component. Therefore, it is an object of the invention to verify the quality of or detecting anomalies in radioactive components by comparing the neutron transmission characteristics thereof with the neutron transmission characteristics of a similar component of known quality, for example, with a factory tested and verified standard component.
Another object is to determine the neutron transmission characteristics of a component.
Another object is to remotely scan a radioactive component submerged in a body of water for neutron transmission therethrough along its length.
Another object of the invention is to provide test equipment including a neutron source and neutron detectors for directing neutrons into and detecting the neutron transmission through a selected dimension of a component.